The measurement of the blood cell counts in a centrifuged sample of anticoagulated whole blood has been described in the scientific literature, and a method for easily measuring certain blood cell and other constituent layers is described in U.S. Pat. No. 4,027,660, granted Jun. 7, 1977 to Stephen C. Wardlaw et al. In the patented method, a sample of anticoagulated whole blood is centrifuged in a precision capillary tube which contains a plastic float. The float linearly expands some of the cell layers and the platelet layer.
In performing the patented method, the blood sample is centrifuged for about five minutes at about 12,000 RPM, and then the expanded lengths of the cell and platelet layers are measured. One of the problems in the patented method pertains to the relatively high centrifuge RPM required to reliably compact the layers, particularly the platelet layer. If the constituent layers are not completely or uniformly packed, the results derived by the method may be inaccurate. The aforesaid high RPM centrifugation requires an expensive centrifuge, and increases the risk of tube breakage. Another problem relates to the required minimum five minute centrifugation time period, which is undesirable in many medical situations. Still another problem relates to the need for the operator to remove the tube from the centrifuge and re-insert it into a reader. Because this operation must be performed within a limited time interval following centrifugation, it requires the close attendance of the operator, which is inefficient and further exposes the operator to a potentially hazardous sample.
It would be desirable to be able to measure the blood constituent layers in a shorter period of time, and with a lower RPM centrifuge, and/or to reduce the amount of sample tube handling.